Image pickup tube semiconductor target support structure

ABSTRACT

An image intensifier vidicon which is divided by a semiconductor target into an image section, the inner surface of the face plate of which is coated with an electron-emissive layer and a scanning section, wherein said semi-conductor target includes a semiconductor substrate, a plurality of PN junctions formed therein, an accelerating layer formed on the electron incident side of said target, and a scanning surface which is protected from contamination by alkali metals constituting the electronemissive layer by means of insulation rings provided in the scanning section. One of the insulation rings also set the critical spacing between the target and a mesh electrode.

Unlted States Patent [151 3,702,410 Miyashiro et al. 1 1 Nov. 7, 1972[54] IMAGE PICKUP TUBE 3,325,672 6/1967 Funahashi et al....3l3/65 A XSEMICONDUCTOR TARGET SUPPORT 3,419,746 12/1968 Crowe et al ..313/66 XSTRUCTURE FOREIGN PATENTS OR APPLICATIONS [72] 1mm: l, 9f 1,041,2259/1966 Great Britain ..313/65 A "!3" 9 K 1,097,587 1/1968 Great Britain..313/65 A TSIJJI, Fu isawa, all of Japan [73] Assignee: Tokyo ShibauraElectric Co., Ltd., Primary EXami'1er-Rbeft5ega] Kawasaki shi, JapanAttorney-Flynn & Frishauf [22] Filed: April 20, 1971 [57] ABSTRACT PP135,710 An image intensifier vidicon which is divided by a semiconductortarget into an image section, the inner Related Apphcmon Data surface ofthe face plate of which is coated with an [63] Continuation-impart f S N889,756, D electron-emissive layer and a scanning section, 31, 1969,abandoned wherein said semi-conductor target includes a semiconductorsubstrate, a plurality of PN junctions [30] Foreign Appncafion priorityData formed therein, an accelerating layer formed on the electronincident side of said target, and a scanning 1969 Japan 8 surface whichis protected from contamination by al- 7, 1969 Japan -44/8697 kalimetals constituting the electron-emissive layer by April 2, 1969 Japan..44/25425 means f insulation rings provided in the scanning c- 1 tion.One of the insulation rings also set the critical [52] U.S. Cl...313/66, 313/82, 313/285 spacing between the target and a meshelectrode. [51] Int. Cl. ..H0lj 31/28, l-lOlj 29/02, HOlj 31/38 [58]Field of Search ..313/65 A, 66

[56] References Cited 11 Claims, 6 Drawing Figures UNITED STATES PATENTS3,073,981 1/1963 Miller et al. ..313/65 A PAIENTEDmv H912 3.702.410

SHEET 1 OF 2 FIG. 1

FIG. 2

34133 262329 VFIG- 4 FIG.'6

IMAGE PICKUP TUBE SEMICONDUCTOR TARGET SUPPORT STRUCTURE CROSS-REFERENCETO RELATED APPLICATION This is a Continuation-impart application of ourcopending application, Ser. No. 889,756, filed on Dec. 3 l, 1969, nowabandoned.

BACKGROUND OF THE INVENTION:

an electron-emissive surface, light entering it beingconverted tophotoelectrons which are further accelerated, and another sectionwherein there is provided an electron multiplication target and saidaccelerated photoelectrons entering said target being taken out in theform of electrical signals by electron beam scanning.

Such an electron multiplication target is generally made of ionconducting glass or electron conducting glass.

An image pickup tube using a target formed of the aforementionedmaterial could not be expected to fully effect the electronmultiplication thereby resulting in the lack of sensitivity.Furthermore, said target is apt to be damaged in use.

The object of this invention is to provide an image pickup tubecomprising an image intensifier section, scanning section and asemiconductor target, which is capable of effecting high sensitivity andhas the target least liable to be damaged in high contrast.

SUMMARY OF THE INVENTION An image pickup tube according to the inventioncomprising an image intensifier section and scanning section has asemiconductor target provided with an accelerating layer foraccelerating carriers produced by impingement of electrons. An imagepickup tube using a semiconductor target which is not provided with suchan accelerating layer can not display full sensitivity and highcontrast, because the electrons entering said target have extremelysmall energy. Further, mere substitution of the aforesaid semiconductortarget with an accelerating layer for the conventional glass target cannot realize the desired effect. The reason is that when theelectron-emissive surface of an image intensifier section or imagesection is activated by alkali metals as is generally practised, saidalkali metals are likely to be critical spacing between the target and amesh electrode.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional viewof an intensifier vidicon according to an embodiment of the presentinvention;

FIG. 2 represents, partly in section, a part of the vidicon of FIGQI,that is, an electron multiplication target and its support member;

FIG. 3 shows perspective views, with part broken away, of thedismembered elements constituting a part of the vidicon of FIG. 1;

FIG. 4 is a sectional view of a form of electron multiplication targetused in the vidicon of FIG. 3;

FIG. 5 is a sectional view of another form of said target; and

FIG. 6 is a sectional view of still another form of said target whereinthere is formed a metal layer on one side of the substrate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS There will now be described byreference to the drawings an electron multiplication target according toan embodiment of the present invention and an intensifier vidiconincluding said target.

Referring to FIG. 1, numeral 10 represents an evacuated envelope, whichis divided into a scanning section 12 and an image section or imageintensifier section 13 with the later described semiconductor electronmultiplication target interposed therebetween. Said scanning section 12comprises an electron gun assembly 14 disposed at one end of theenvelope 10, a long cylindrical grid electrode 15 located ahead of saidassembly 14 and a field mesh electrode 16 stretched across the frontopening of said electrode 15. Said image section 13 comprises anelectron-emissive surface 18 formed on the inner wall surface of thefront or face plate 17 of said envelope 10, first and second cylindricalelectrodes 19 and 20 for focusing and accelerating electrons emittedfrom said electron-emissive film 18 or primary electrons and saidelectron multiplication target 21 disposed behind these two electrodesl9 and 20 which will be further described later. This electronmultiplication target is so positioned as to optically shut off saidscanning section 12 and image section 13 from each other.

There will now be described concrete shielding means by reference toFIGS. 2 and 3. On the outer periphery near the opening of the largediameter section 22 of said grid electrode 15 is coaxially fixed anannular insulation member 23 by cylindrical metal stoppers 24 and 25having an L-shaped cross section which are disposed on both sides ofsaid insulation member 23 respectively, and fixed to said large diametersection 22, for example, by spot welding. On the large diameter section22 of said grid electrode 15 is mounted a cylindrical target support 27constituting a target electrode. Said support 27 has an inner diameterto match the outer diameter of the aforesaid insulation member 23 andincludes an annular metal stopper 26 having an L shaped cross sectionand coaxially fitted to the inner wall of the support 27. This support27 and the aforesaid large diameter section 22 of the grid electrode arefixed to each other by clamping the end portion of said annularinsulation member 23 between diameter portion 31 inserted into the openend part of the large diameter section 22 of said grid electrode.Further inside of said cylindrical target support 27 are coaxiallyarranged in turn a cylindrical insulation member 32 whose outer diameterfits the inner diameter of the target support 27 and whose innerdiameter is smaller than the outer diameter of said mesh electrode 16,an annular spring electrode 33 and said target 21. To the foremost endof the target support 27 is welded an annular metal stopper 34 having anL-shaped cross section. The interval between the field mesh electrode 16and target 21 is defined by the length of said cylindrical insulationmember 32. The cylindrical insulation members 23 and 32 may be made of,for example, ceramic. Said target 21 and its cylindrical target support27 are electrically connected by the projections formed on said springelectrode 33. The mesh electrode 16 is interposed, as shown in FIG. 2,between a washer 35 fitted to said cylindrical insulation member 32 anda spring electrode 36. Said mesh electrode 16 is further electricallyconnected to said grid electrode 15 through said spring electrode 36.

The shielding means of the aforementioned construction is capable of notonly optically shielding the image and scanning sections from each otherby two insulation members 23 and 32, but also protecting the scanningsurface of the semiconductor target from contamination. With theintensifier vidicon, an electronemissive layer has heretofore beenformed by thermally evaporating electron-emissive materials and alkalimetals on the inner surface of the front part of the intensifiersection. In this case, it was impossible to scanning section of thetarget.

According to the image pickup device of this invention, however, thereare-disposed near the end of a long cylindrical electrode a cylindricalsupporting member 27 and two insulation members 23 and 32 at prescribedintervals, thereby substantially preventing said alkali metals frombeing deposited on the scanning surface of the target. Oneinsulationmember 23 is intended to prevent the alkali metals fromintruding into the scanning section through the interstice between thecylindrical member 27 and envelope 10. The other insulation member 32 isused to prevent said alkali metals from being conducted into thescanning section through the interstice between the target 21 andcylindrical member 27. The latter insulation member 32 concurrentlyplays, as described above, the role of defining the distance between thetarget and mesh electrode.

There will now be described the aforementioned electron multiplicationtarget 21 by reference to FIG. 4. This target is formed of an N-typeconductivity silicon substrate 40 having, for example, a specificresistance of lOQ-cm. On one side of said substrate 40 are formed aplurality of :P-type conductivity small regions 41 at a prescribed spaceby selective diffusion of prevent the deposition of said alkali metalson the boronso as to define PN junctions 42 between said N- typesubstrate 40 and P-type regions 41. One side of said substrate exceptthe P-type regions is coated with a protective film 43 of insulationmaterial, for example, silicon dioxide. Further on the same side of saidsubstrate 40 is mounted a film of antimony selenide 44 about 500 A thickin a manner to cover said protective film 43 and P-type regions 41 inorder to prevent said protective film 43 from being unnecessarilycharged. Obviously, said antimony selenide film 44 should have asufficientlyhigh resistance to prevent the resolution of said target 21from being obstructed. On the other side of said substrate 40, namely,that side thereof into which there are introduced image photoelectrons,there is formed by diffusion an impurity layer 0.5 microns deepconsisting of a high concentration of phosphorus, namely an N -typeconductivity layer 45, thus resulting in a potential gradient betweensaid substrate 40 and N -type conductivity layer 45.

A targetaccording to the present invention is not limited to the typehaving the aforesaid diode construction, but may be of, for example,transistor construction. FIG. 5 represents a concrete example of thelatter construction. The same parts of the figure as those of theaforesaid embodiment aredenoted by the same numerals and descriptionthereof is omitted. On one side of an N-type conductivity siliconsubstrate 40'is formed an N -type conductivity layer 45 and on the otherside an insulation film 43 and a semi-insulating film 44, for examplemade of antimony selenide or antimony sulfide, as shown, in the samemanner as used in the preceding embodiment. On that side of thesubstrate on which there is deposited said insulation film 43 there areformed by selective diffusion a plurality of P-type conductivity mosaicregions 46 at a prescribed space.

In each of said P type conductivity regions is formed an N-typeconductivity region 47. As a result, said P-type and N-type conductivityregions 46 and 47 and substrate jointly for-m N-P-N construction.

With the aforementioned device, there is defined a potential gradientbetween said N-type conductivity substrate and the N -type conductivitylayer formed on that side of said substrate into which there are introduced image photoelectrons. Said potential gradient allows minoritycarriers generated by introduction of said image photoelectrons into thesubstrate to proceed to the PN junctions at an accelerated speed, thuspreventing the possibility of said minority carriers being extinguishedwhile travelling to said PN junctions, thereby effectively amplifyingsaid image photoelectrons to a far greater degree than is possible withany prior art device.

According to the present invention there is formed in a semiconductorsubstrate a region capable of accelerating minority carriers. Saidregion may be prepared not only by the aforesaid diffusion method, butalso, for example, in the following manner, as concretely illustrated inFIG. 6. The same parts of FIG. 6 as those of the aforementionedembodimentsare denoted by the same numerals and description thereof isomitted. On one side of an N-type conductivity silicon substrate 40 areformed a plurality of P-type conductivity regions 41 2 microns deep at aprescribed space so as to define PN junction 42 with said substrate 40.On the first mentioned side of said substrate 40 is formed an insulationfilm, for example, of silicon diox ide or silicon nitride in a manner tocover the exposed part of each PN junction 42. On the remaining exposedparts of said side of the substrate, namely, on the surface of eachP-type conductivity region 41 and also on said insulation film 43 thereis deposited a film of antimony sulfide 44 about 500 A thick. On theother side of said substrate 40, namely, that side thereof into whichthere are introduced image photoelectrons, there is deposited a metallayer 48 having a thickness of several hundred A units, namely, athickness sufficiently small to allow electrons to penetratetherethrough which are accelerated with several kilovolts or ten and oddkilovolts. Since said metal layer 48 consists of a material displaying asmaller work function than the silicon constituting said substrate, forexample, aluminum or antimony, there prevails a potential gradientbetween said metal layer 48 and substrate 40, obtaining the same effectas in the aforesaid embodiments. It will be apparent that where saidsubstrate 40 is of P-type conductivity, then use of a substanceexhibiting a larger work function than the material of said substrate,for example, tellurium, indium or platinum, will generate the samepotential gradient as described above.

The target according to the last mentioned embodiment not only has thesame effect as that of the preceding ones, namely, the effect ofprominently amplifying image photoelectrons, but also can be expected tooffer the following advantages.

The metal layer deposited on that side of the substrate into which thereare introduced image photoelectrons allows said electrons to proceed tothe substrate without exerting any harmful effect thereon, whereas saidmetal layer serves the purpose of shielding any extra light. As aresult, minority carriers are only generated in the substrate byimage-forming electrons, enabling the image pickup tube of the presentinvention to perform excellent resolution.

However, the prior art device has the drawbacks that where there isformed a face plate or photoelectric plate in the image section of thepickup tube by the deposition of an electron-emissive material, and theactivation of alkali metals for example, cesium, that side of the targeton which there are introduced image electrons is eventually contaminatedby the cesium, thereby decreasing properties of said target. Forexample, where the device is of a diode construction, there will fallthe yield voltage, or increase the dark current. In contradistinction tothis, the target according to the last mentioned embodiment wherein themetal layer acts as a protective film is saved from the aforesaiddeterioration of properties.

In all the above-mentioned embodiments the target substrate consisted ofsilicon, but the target may be prepared from other semiconductormaterials, for example, germanium or gallium arsenide. Further, thesubstrate may be of P-type conductivity instead of N- type conductivityas used in the foregoing embodiments. in this case, however, theaforementioned island regions should, of course, be of N-typeconductivity.

What we claim is:

1. An image pickup tube comprising an evacuated envelope, an electrongun disposed at one end of said envelope, a cylindrical electrode foraccelerating electron beams from said electron gun, a cylindricalsupporting'member within said envelope having a diameter larger than theaccelerating electrode, the supporting member and the acceleratingelectrode being fitted into each other at mutually facing end portionsand coaxially disposed in the envelope, a field mesh electrodepositioned in the supporting member to close the open end of thecylindrical accelerating electrode, a semiconductor target positioned inthe supporting member spaced from and facing the mesh electrode, a pairof annular insulation members, one of which is interposed between thecylindrical supporting member and the accelerating electrode and theother of which is sandwiched between the peripheral portions of saidtarget and said mesh electrode to define a predetermined spacingtherebetween, an electrode to define a predetermined spacingtherebetween, an electronemissive surface provided on the other end ofsaid envelope to convert the light of an image to electrons andelectrode means provided between the electron-emissive surface and thetarget to accelerate said electrons and focus them on the target, thesemiconductor target comprising a semiconductor substrate having aplurality of PN junctions formed on the scanning side of said substratefacing said electron gun and an accelerating layer formed on the imageelectron incident side of said substrate.

2. The image pickup tube according to claim 1 wherein said acceleratinglayer has the same type of conductivity as, but contains a higherconcentration of impurities than, said substrate.

3. The image pickup tube according to claim 2 wherein said substrate andaccelerating layer are of N- type conductivity.

4. The image pickup tube according to claim 1 wherein said targetincludes a metal film on the image electron incident side of thesubstrate to form said accelerating layer between the substrate andmetal layer.

5. The image pickup tube according to claim 1 wherein said targetincludes a plurality of first separate regions on one side of saidsubstrate having one type of conductivity whose conductivity is ofopposite type to said substrate, thereby defining PN junctions betweensaid substrate and regions.

6. The image pickup tube according to claim 5 wherein said targetincludes a plurality of second separate regions respectively formed insaid first regions, the second regions having opposite type ofconductivity from the first regions thereby defining PN junction betweenthe first and second regions.

7. The image pickup tube according to claim 5 wherein said targetincludes an insulating layer on the image electron incident side of thesubstrate except on said first separate regions.

8. The image pickup tube according to claim 7 wherein said targetincludes a semi-insulating film on the insulating layer and firstseparate regions.

9. The image pickup tube according to claim 1 wherein said insulationmembers are made of ceramic.

10. The image pickup tube according to claim 1 wherein said insulationmembers are spaced from each other along the axis of said cylindricalsupporting member, said other insulation member preventing alkalaimetals from being conducted into the scanning section through theinterstice between the cylindrical supporting member and the target.

11. The image pickup tube according to claim 1 wherein the cylindricalsupport member and the accelerating electrode have annular stoppermembers extending therefrom, said one insulation member being interposedbetween said stopper members. 5

1. An image pickup tube comprising an evacuated envelope, an electrongun disposed at one end of said envelope, a cylindrical electrode foraccelerating electron beams from said electron gun, a cylindricalsupporting member within said envelope having a diameter larger than theaccelerating electrode, the supporting member and the acceleratingelectrode being fitted into each other at mutually facing end portionsand coaxially disposed in the envelope, a field mesh electrodepositioned in the supporting member to close the open end of thecylindrical accelerating electrode, a semiconductor target positioned inthe supporting member spaced from and facing the mesh electrode, a pairof annular insulation members, one of which is interposed between thecylindrical supporting member and the accelerating electrode and theother of which is sandwiched between the peripheral portions of saidtarget and said mesh electrode to define a predetermined spacingtherebetween, an electrode to define a predetermined spacingtherebetween, an electron-emissive surface provided on the other end ofsaid envelope to convert the light of an image to electrons andelectrode means provided between the electron-emissive surface and thetarget to accelerate said electrons and focus them on the target, thesemiconductor target comprising a semiconductor substrate having aplurality of PN junctions formed on the scanning side of said substratefacing said electron gun and an accelerating layer formed on the imageelectron incident side of said substrate.
 2. The image pickup tubeaccording to claim 1 wherein said accelerating layer has the same typeof conductivity as, but contains a higher concentration of impuritiesthan, said substrate.
 3. The image pickup tube according to claim 2wherein said substrate and accelerating layer are of N-typeconductivity.
 4. The image pickup tube according to claim 1 wherein saidtarget includes a metal film on the image electron incident side of thesubstrate to form said accelerating layer between the substrate andmetal layer.
 5. The image pickup tube according to claim 1 wherein saidtarget includes a plurality of first separate regions on one side ofsaid substrate having one type of conductivity whose conductivity is ofopposite type to said substrate, thereby defining PN junctions betweEnsaid substrate and regions.
 6. The image pickup tube according to claim5 wherein said target includes a plurality of second separate regionsrespectively formed in said first regions, the second regions havingopposite type of conductivity from the first regions thereby defining PNjunction between the first and second regions.
 7. The image pickup tubeaccording to claim 5 wherein said target includes an insulating layer onthe image electron incident side of the substrate except on said firstseparate regions.
 8. The image pickup tube according to claim 7 whereinsaid target includes a semi-insulating film on the insulating layer andfirst separate regions.
 9. The image pickup tube according to claim 1wherein said insulation members are made of ceramic.
 10. The imagepickup tube according to claim 1 wherein said insulation members arespaced from each other along the axis of said cylindrical supportingmember, said other insulation member preventing alkalai metals frombeing conducted into the scanning section through the interstice betweenthe cylindrical supporting member and the target.
 11. The image pickuptube according to claim 1 wherein the cylindrical support member and theaccelerating electrode have annular stopper members extending therefrom,said one insulation member being interposed between said stoppermembers.